Digitizer systems are used as computer input devices for capturing data or handwritten signatures, text, drawings, symbols or the like. Digitizing tablets and/or touch screens are exemplary digitizer systems used to replace a mouse as a primary pointing and navigation device for desktop computers. A user interacts with the digitizer system by positioning and moving an object such as stylus and/or a finger over a sensing surface of the system, e.g. a tablet and/or a touch screen. Position of the object with respect to the sensing surface is tracked by the digitizer system and interpreted as a user command. An electromagnetic stylus is one type of stylus known in the art for operating a digitizer system. The electromagnetic stylus operates by emitting an electromagnetic signal that can be picked up at locations on the sensing surface of the system. Position detection can typically be performed while the object is either touching and/or hovering over the sensing surface.
U.S. Pat. No. 6,690,156 entitled “Physical Object Location Apparatus and Method and a Platform using the same,” U.S. Pat. No. 7,292,229 entitled “Transparent Digitizer,” and U.S. Pat. No. 7,372,455 entitled “Touch Detection for a Digitizer,” all of which are assigned to N-trig Ltd., the contents of all of which are incorporated herein by reference, describe a device for detecting objects disposed in association with a graphical display device. The device includes a transparent sensing arrangement of detectors located on the display screen that provide output to detect a location of the object in relation to the display screen.
In U.S. Pat. No. 7,292,229 there is also described an electromagnetic stylus designed to generate an electric field concentration in the vicinity of the front tip so that a location of the stylus with respect to the display screen can be accurately determined. It is described that the stylus can optionally also generate an electric field concentration in the vicinity a reverse tip located at a second end remote from the front tip for detecting location during an eraser event. Variations in the electric field generated at each of the tips can be introduced to differentiate between an eraser event and a front tip event.
U.S. Patent Application Publication No. 20080128180 entitled “Position Detecting System and Apparatuses and Methods for Use and Control Thereof,” assigned to N-Trig Ltd, which is incorporated herein by reference, describes a pointer such as an electromagnetic stylus including a wave generating oscillator section for generating a signal to be detected by a digitizer sensor. Although, the wave generating oscillator section can be powered by an energy pick-up circuit, it is able to generate signals with a frequency that is independent from a frequency of the energy pick-up circuit.
U.S. Patent Application Publication No. 20080012835 entitled “Hover and Touch Detection for a Digitizer,” assigned to N-trig Ltd, which is incorporated herein by reference, describes a system and method using both touch and hover of an object to interact with a digitizer sensor. It is described that a detected and/or recognized hover input signals can be implemented for controlling cursor position, for predicting the oncoming of a finger touch event, and for distinguishing between touch intended for user interaction and touch not intended for user interaction. A method for distinguishing between a touch and hover event based on a spatial pattern of signals received on the digitizer sensor is described.
U.S. Patent Application Publication No. 20100051356 entitled “Pressure Sensitive Stylus for a Digitizer,” assigned to N-trig Ltd, which is incorporated herein by reference, describes a stylus including an optical sensor enclosed within a housing of the stylus for optically sensing displacement of a tip of the stylus in response to applied contact pressure.
U.S. Pat. No. 6,489,899 entitled “Position Detector,” which is incorporated herein by reference, describes a digitizer system including a multiplicity of loop coils arranged in parallel with one another in X- and Y-directions for detecting position and orientation of a magnetic field generator embedded in an object such as a stylus or a game piece used for interacting with the digitizer system. Each of the loop coils is described to extend over a sensing surface in a geometrically varying manner having different characteristic dimensions along the measurement path so that relative position and orientation of the object in a sensing plane of the digitizer can be determined. There is also described a game piece that includes two magnetic field generators separated from each other by a predetermined distance and which are operable to generate different magnetic fields in substantially different directions. It is described that complete relative orientation between the sensor and an object including two magnetic field generators can be determined based on determined position and orientation of each of the generators along the sensor surface.